A modem is a device that allows both voice and data communications to be transmitted over a single telephone line. A computer that transmits and receives data can be used to access various data banks and computer services that are available. From time to time, a situation can occur wherein an incoming call occurs while the computer or telephone set is in use. Ordinarily, the calling party gets a busy signal and the called party is not aware that a call is being attempted. Understandably, some calls are more important than others, and many users desire to know that an incoming call is being attempted.
Some telephone central offices offer a call waiting feature that alerts a telephone user that a third party is trying to call the user. In such a system, the user can interrupt the waiting call and take the call from the third party to determine whether the second call is more important than the ongoing call. Typically, when a modem is used, the call waiting feature is lost because the modem is not adapted to respond to the call waiting signal. Accordingly, it will be appreciated that it would be highly desirable to have a modem adapted to accommodate a call waiting feature so that the user can be alerted when a third party is trying to complete a call.